Second part of tennis match, losing with a fight (3-2)
I believe the answer is:
set-to
'a fight' is the definition.
(I know that set-to is a type of fight)
'second part of tennis match losing with' is the wordplay.
'second part of tennis match' becomes 'set two' (the second set).
'losing' indicates named letters should be taken away.
'with' becomes 'w' (abbreviation).
'settwo' with 'w' taken out is 'SET-TO'.
(Other definitions for set-to that I've seen before include "brush with violence?" , "Altercation" , "Fight, argument" , "Ready - fight" , "Scrap" .)